Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $150.59   12.264%   $169.0584   $169.06   $169.05   $169.10  
  Purchase #2 $175.87   9.551%   $192.6673   $192.67   $192.65   $192.70  
  Purchase #3 $232.91   4.860%   $244.2294   $244.23   $244.25   $244.20  
  Purchase #4 $101.81   11.339%   $113.3542   $113.35   $113.35   $113.40  
  Purchase #5 $181.62   6.469%   $193.369   $193.37   $193.35   $193.40  
  Purchase #6 $114.60   4.683%   $119.9667   $119.97   $119.95   $120.00  
  Purchase #7 $13.73   7.504%   $14.7603   $14.76   $14.75   $14.80  
  7 purchase totals = $971.13       $1,047.4053   $1,047.41   $1,047.35   $1,047.60